1. Field of the Invention
The present invention relates to a break-resistant multiribbed plate of impact-resistant polymethacrylate SP, having high hail resistance.
2. Discussion of the Background
Multiribbed plates made of polymethyl methacrylate plastics are known. Especially for vitrification, multiribbed plates of polymethyl methacrylate plastics are used due to their higher translucence and greater resistance to weathering.
DE-OS 3,011,905 describes window elements of double-ribbed plates which combine translucence and light-reflective properties and have insulating intermediary spaces containing static air in order to delay transfer of heat through the window elements. The disclosed ribs in the double-ribbed plates are arranged geometrically and vary in their translucencies such that the intensity of the solar radiation after penetration through the window elements varies as a function of the height of the sun. The window elements are preferably made of acrylic polymers, especially polymethyl methacrylate.
In U.S. Pat. No. 4,114,597, solar collectors are described which consist of triple-ribbed plates in which the hollow chamber layer facing the sun is filled with air and the hollow chamber layer turned away from the sun is filled with a heat-transfer medium which absorbs the solar energy. The triple-ribbed plates consist preferably of polymethyl methacrylate plastic due to its high transparency and resistance to weathering.
DE-OS 3,147,113 includes double-ribbed plates which contain illuminants located in the hollow chambers and which consist of break- and impact-resistant plastics which are not specified in more detail. The demand for break resistance and impact resistance is based on the application of the double-ribbed plates as floors or wall elements.
Polymethyl methacrylate is known to be a comparatively brittle plastic, sensitive to impact, which causes a reduced mechanical loadability of multiribbed plates made from polymethyl methacrylate plastic. In DE-OS 3,011,905 and U.S. Pat. No. 4,114,597, the use of impact-resistant, modified polymethyl methacrylate plastics as "material" for multiribbed plates is vaguely suggested (DE-OS 3,011,905, page 20, lines 35-37; U.S. Pat. No. 4,114,597, column 4, lines 34-40), but no data on the chemical composition and mechanical properties as well as on the minimum requirements in mechanical properties of such modified polymethyl methacrylate plastics is given.
EP-A 0,105,159 and EP-A 0,118,683 are also concerned with the problem of brittleness in multiribbed plates or polymethyl methacrylate plastics.
EP-A 0,105,159 describes multiribbed plates having parallel, flat outer layers of polymethyl methacrylate, with at least one middle layer. The plates have ribs in which the outer layers and the middle layer are connected with one another as one piece. The middle layer is constructed of a plastic with increased toughness and/or elevated zero shear-rate viscosity in the molten state, compared to the polymethyl methacrylate plastic. Due to the middle layer, the toughness of the multiribbed plate is increased, and especially, sagging of the middle layer during extrusion of the total compound is avoided or reduced.
In EP-A 0,118,683, multilayer, coextruded double-ribbed plates with reduced sensitivity to impact are disclosed. The plates contain two essentially flat outer walls with ribs connecting them as one piece. More than half of the entire thickness of the supporting layer of the outer wall consists of an acrylic glass, especially of polymethyl methacrylate plastic, and the inner side of the acrylic glass layer consists of a thinner inner layer combined adhesively with a plastic having a higher elongation at break, such as polycarbonate.
Both in EP-A 0,105,159 as well as in EP-A 0,118,683, the use of impact-resistant, modified polymethyl methacrylate plastic (EP-A 0,105,159, page 2, lines 21 and 22; EP-A 0,118,683, page 4, lines 10ff) is mentioned. Nevertheless, the method of production of the double-ribbed plates described there is associated with high equipment outlay. Furthermore, the tough plastics used in EP-A 0,105,159 and in EP-A 0,118,683 to reduce sensitivity to impact, such as, polycarbonates, polyesters, or polysulfones, are to a large extend detrimentally affected by weather, especially UV radiation, and must be stabilized accordingly.